Transcript Evaporative Emissions Control Systems (EVAP)

Evaporative Emissions Control
Systems (EVAP)
•Purpose
•Enhanced
and Non-Enhanced
•Components
•Function
•Finding Faults
Purpose:
 To
trap and hold gasoline vapors (HC)
 To deliver vapors to engine airflow for complete
burning
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Provides system ventilation to allow purging
Provides pressure relief to prevent excess pressure
inside fuel tank
2 Types of Systems
 Non-Enhanced
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Diagnostic ability is limited to purge
detection and monitoring
 Enhanced
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Monitors purge flow
Monitors system integrity
Leak checking
1996-2000: leak checking to .040 in.
2000-up: leak checking to .020 in.
Components:
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Carbon canister
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Purge valve/ Purge solenoid
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Seals fuel tank
Allows for pressure relief
Prevents excessive vacuum from collapsing tank
Fuel expansion tank
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Connect tank to canister
Connect canister to engine
Fuel tank filler cap
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Controlled by PCM to allow canister purging during certain
conditions
Vacuum lines
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Traps and holds fuel vapors for burning by engine
Prevents liquid fuel from entering canister
Fuel Tank Pressure Sensor (Enhanced)
Vent valve (Enhanced)
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Provides fresh air for system purging
Can be used to seal system to check for leaks
Function:
 As
fuel heats up: vapors form and are
vented to canister
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Canister is filled with activated charcoal
Fuel vapors attach to carbon surface
1 gram of charcoal contains surface area
equal to ¼ acre
Holds 1/3 of its own weight in fuel vapors
 As
system is purged, vapor molecules are
pulled from carbon surface
Function:
 Pressure
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build-up is caused by:
Volatility rates
Fuel tank size
Fuel level inside tank
Fuel slosh
Temperature
Fuel return
Function:
 Purging
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Excess fuel vapors can upset air/fuel ratio
 Purging
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is allowed:
Closed loop
Cruising speeds
 Purging
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is closely controlled
is not allowed:
Open loop
Idle or deceleration
WOT
Finding Faults
 Two
types of complaints:
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Fuel vapor smell
MIL illumination
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Check freeze frame data for ECT and VSS
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Purge control circuit failures
Purge flow failures
Leak detection DTC’s
 Retrieve
 Check
 DTC’s:
DTC’s
TSB‘s, recalls and PCM reflashes
Finding Faults
 Follow
manufacturer’s diagnostic
troubleshooting procedure
 Purge control circuit failures: can be
checked with bidirectional scan tool
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Command purge valve on and listen for clicking
sound
With valve commanded on check for air flow
through valve
 Check
power and ground wires with
voltmeter
 Purge valve can be manually activated
with jumper wires
Finding Faults
 Purge
flow failures: can be caused by
leakage or restriction preventing purge
 Smoke machine: insert probe into test port
and watch machine’s flow meter
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Proper flow eliminates possibility of
restriction in system
Improper flow indicates system is restricted:
isolate system and continue checking
Finding Faults
 Leak
checks: connect smoke machine
and close vent solenoid
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Vent solenoid can be closed with scan tool,
manually cycled with jumper wires or vent
pinched with suitable tool
Smoke machine should indicate no flow if
system is free from leaks
If leaks are present, smoke will be visible
Locating Leaks
 Smoke
testing: uses low pressure smoke
introduced to system from test port
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Allows for visual leak detection
 Nitrogen
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gas pressurization
Very low pressure (> 1 psi)
Uses sound amplification for detecting leaks
Toyota Evaporative Emissions